A bumper is mounted on a front end portion of a vehicle. The bumper is provided, inside thereof, with a bumper beam for absorbing impact at the time of collision.
A bumper is normally provided with a bumper reinforcement member to be mounted on a front of a vehicle so as to extend in a vehicle width direction and a pair of right and left crush boxes for supporting the bumper reinforcement member on a vehicle structure. The bumper beam is configured to be deformed itself to thereby absorb collision energy. Absorbing the collision energy results in reduced damages of vehicle parts other than the bumper beam.
In such a bumper beam, a bumper reinforcement member and a crush box are usually secured with each other by welding or bolting. Fixing the bumper reinforcement member and the crush box by welding may sometimes increase in cost. Fixing the bumper reinforcement member and the crush box by bolding may sometimes result in unexpected shear fracture at the time of collision.
To solve the problems, conventionally proposed is a method of fixing a bumper reinforcement member and a crush box not by means of welding or bolting.
In a bumper shown in the following Patent Document 1 for example, through-holes are formed so as to penetrate a bumper reinforcement member. With a crush box arranged in the through-holes in a penetrated manner, the crush box is subjected to a tube expanding process by means of electromagnetic forming. With this, the bumper reinforcement member and the crush box are secured with each other.